The present invention relates to a superconducting magnet and a method of manufacture thereof.
With the superconducting magnet of today, by holding a coil structure including a superconducting wire to be in the superconducting state, no potential difference is produced across the coil structure, and the electric resistance is substantially zero. Thus, once current is supplied to the coil structure, the coil structure can carry current continually for a very long period of time (this state being referred to as "permanent current state") even when the power source is subsequently disconnected. The density of current that can be passed through the superconducting coil, while maintaining the zero electric resistance state, is very high, about 100 times, compared to the case of the coil in the normal state.
The superconducting magnet having the above property finds very extensive applications; for example it is used as a nuclear fusion plasma shut-off electromagnet, a high energy particle acceleration electromagnet, a train side permanent magnet for a magnetically levitated train, a generator rotor electromagnet, etc.
In the superconducting magnet of prior art, for instance a superconducting magnet for magnetically levitated train, the superconducting coil is race track shaped and has a rectangular sectional profile. It is impregnated with a hardenable material such as an epoxy resin and is accommodated in a vessel member. The vessel member is also race track shaped and isolates the coil from atmospheric conditions. Inside the vessel member, the superconducting coil is supported at discontinuous points by a plurality of spacers. The annular inner space of the vessel member is partitioned by a plurality of spacer plates into a plurality of chambers. The spacer plates are each provided with openings. Coolant such as liquid helium is caused to pass through the chambers by clearing the openings. The superconducting coil structure is thus held cooled to be lower than the transition temperature thereof.
However, with the prior art superconducting magnet as described above, in which the coil structure is directly and discontinuously supported by the spacer plates (over narrow support areas corresponding to the thickness of the spacer plates), the mechanical strength of the support with respect to electromagnetic force is insufficient. Particularly, with the superconducting magnet for magnetically levitated train where strong vibrations are experienced, rattling or looseness is liable to result between the coil structure and spacer plates, and this leads to a hazard of instable securement of the coil. Further, since the superconducting coil is supported at its four sides over a narrow area corresponding to the thickness of the spacer plate, heat of friction is liable to be generated in the coil support regions due to electromagnetic forces. If the heat of friction is generated, the coil is locally heated to result in an undesired result of its state change from the superconducting state to the normal state (this phenomenon being referred to as "coil quench").
Further, when manufacturing the aforementioned prior art superconducting magnet, it is necessary to mount a plurality of spacer plates on the coil and fix them to the vessel member. Therefore, the productivity in manufacture is inferior, causing manufacturing cost of the superconducting magnet to become high. Further, in the prior art manufacture of the superconducting magnet, the superconducting coil has to be impregnated with the hardenable material such as epoxy resin before setting it in the vessel member. Therefore, the possibility of inflicting adverse effects such as cracks on the impregnated coil structure, due to heat in welding at the time of the assembly, is high. As a result, the property of the coil structure is undesirably caused to deteriorate. Thus, there has been established no satisfactory results in connection with the superconducting magnet and method of manufacture thereof.